Electroless coating method

ABSTRACT

Disclosed is an electroless method for coating a substrate with the oxide of aluminum, gallium, indium or thallium. The method involves contacting the substrate with fumes of a polychloride of titanium, tin or platinum and the hydroxide of aluminum, gallium, indium or thallium to form a layer on the substrate of the metallic polychloride in contact with the metal hydroxide. The treated substrate is then heated in a water vapor bearing atmosphere to decompose the metal hydroxide and leave a coating comprising an oxide of the metal on the substrate.

United States Patent 1191 Herbert ELECTROLESS COATING METHOD [75] Inventor: William Gerard Herbert, Webster,

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22' Filed: Feb. 21, 1974 21 Appl. No.: 444,584

[52] US. Cl. 427/226 [51] Int. Cl B44d 1/12; B44d H14 [58] Field of Search... 117/130 E, 47 R, 49, 169 R,

3,705,051 12/1972 Kobetz et a1 117/47 A 1451 July 15,1975

3,762,938 10/1973 Ridenour et al. 117/160 R Primary ExaminerCameron K. Weiffenbach Assistant Examiner.lohn D. Smith Attorney, Agent, or Firm-James J. Ralabate; James P.

OSullivan; Jerome L. Jeffers [57] ABSTRACT Disclosed is an electroless method for coating a substrate with the oxide of aluminum, gallium, indium or thallium. The. method involves contacting the substrate with fumes of a polychloride of titanium, tin or platinum and the hydroxide of aluminum, gallium, indium or thallium to form a layer on the substrate of the metallic polychloride in contact with the metal hydroxide. The treated substrate is then heated in a water vapor bearing atmosphere to decompose the metal hydroxide and leave a coating comprising an oxide of the metal on the substrate.

13 Claims, No Drawings 1 ELECTROLESS COATING METHOD BACKGROUND OF THE INVENTION There are many situations in which it is desirable to coatthe surface of a solid substrate with an oxide of a group III A metal; i.e. aluminum, gallium, indium or thallium. These metal oxides are useful materials for coating metal articles due to the attractive appearance and corrosion inhibiting properties which can be obtained by applying such a coating. One method of applying a coating of the oxide of a group III A metal is to deposit a coating of the metal by electrochemical means and allow the metal coating to oxidize. However, the application of the metal coating by electrochemical means has proven problematical for the reason that the plating must proceed from an etherate bath with the resultant fire hazard inherent in such a system. Consequently, electroless methods for coating substrates with group III A metals have been sought after. Besides eliminating the aforementioned hazards associated with the use of an ethe'rate bath in electroplating, electroless methods provide the additional advantage of being applicable to nonconductive substrates.

One method of electroless aluminum plating is disclosed in U.S. Pat. No. 3,462,288 in which aluminum hydride is decomposed by contacting it with a decomposition catalyst selected from a compound of a Group [Vb or Vb metal. This process is effective for coating a substrate with a continuous layer of aluminum but suffers from two major disadvantages. The first disadvantage results from the fact that aluminum hydride is a very active composition and presents a serious tire and explosion hazard. The second disadvantage lies in the reactivity of aluminum hydride with water vapor which necessitates the use of a water free atmosphere such as a nitrogen filled dry box for the plating process.

It would be desirable and it is an object of the present invention to provide a novel method for the coating of a substrate with the oxide of a group III A metal.

It is a further object to provide such a method which is electroless in nature.

An additional object is to provide such a process which employs non-flammable, non-explosive materials.

An additional object is to provide such a process which can be carried out under ambient atmospheric conditions.

SUMMARY OF THE INVENTION The present invention is a method for coating a substrate with the oxide of a group III A metal. The method involves:

a. contacting the substrate with fumes of titanium trichloride, titanium tetrachloride, stannic tetrachloride, platinum tetrachloride or a mixture thereof;

b. contacting the substrate with one or more of the hydroxides of aluminum, gallium, indium or thallium to form a layer of the metal hydroxide on the substrate in contact with the metallic polychloride; and

c. heating the treated substrate in a water vapor bearing atmosphere to a temperature sufficient to decompose the metal hydroxide and thereby provide a layer of the oxide of a metal corresponding to the metal of the metal hydroxide on the substrate.

DETAILED DESCRIPTION The process of the present invention is based upon the discovery that contacting a substrate with fumes of certain metal polychlorides will impart a residue of the metal chloride on the substrate which can decompose a group III A metal hydroxide to provide the oxide of the metal. Those metal polychlorides which fume upon exposure to the atmosphere, i.e. titanium trichloride, titanium tetrachloride, stannic tetrachloride and platinum tetrachloride, can readily be applied to the substrate by simply passing it through the fumes of the metal polychloride. The metal polychlorides enumerated herein are very susceptible to hydrolysis and fume strongly when contacted with moist air. Maintaining the substrate in contact with the fumes for at least about 60 seconds is recommended for a substantially complete coating, although shorter contact times may be employed, especially when the fumes of the metallic polychloride are quite dense. The only criteria is that sufficient metallic polychloride adhere to the substrate to cause at least some decomposition of the metal hydroxide. This procedure need not be carried out under any special conditions; however, for safety purposes, a well-ventilated area such as a fume hood is recommended for'thispart of the procedure. Any of the afroementioned metal polychlorides may be used with titanium tetrachloride being preferred.

At this point, the treated substrate is contacted with the metal hydroxide. Any method of contact which provides a reasonably continuous coating may be employed. A preferred method involves cascading a finely ground powder of the metal hydroxide over the substrate. Normally, the substrate is moistened, such as by contacting it with water vapor, in order for the particulate metal hydroxide to adhere to the substrate. Moisture is not essential at this point, however, and any convenient method may be employed to maintain the metal hydroxide in contact with the substrate.

It is not essential that the substrate be contacted with the fumes of the metallic polychloride before applying the metal hydroxide. Since the only requirement is that the metallic tetrachloride be in contact with the metal hydroxide on the surface of the substrate, the application may proceed in any order or simultaneously. The selection of the metal hydroxide to be used will, of course, depend on which metal oxide is desired on the substrate. Each of the group III A metal-oxides, i.e. aluminum, gallium, indium and thallium oxide provide a corrosion inhibiting passive barrier. In addition, a dye may be applied to the metal oxide coating to enhance the appearance of the coated substrate. In certain instances, it may be desirable to apply a coating to the substrate which comprises a mixture of two or more group III A metals. This is readily accomplished by employing a mixture of metal hydroxides in the proper ratio to provide the proper mixture of metals upon decomposition of the hydroxide.

After application of the metallic polychloride and metal hydroxide to the substrate, the treated substrate is heated to a temperature and for a time sufficient to cause conversion of the metal cation of the hydroxide to the metal oxide. Heating time and temperature will depend upon various factors such as the particular metallic polychloride and metal hydroxide being employed as well as the particle size of the metal hydroxide. In addition, the time and temperature will vary in an inverse relationship with each other. Normally, heating the treated substrate to a temperature of from 50 to C. for a period of at least about 1 minute will be sufficient to cause complete reaction of the metal hydroxide with subsequent deposition of the metal oxide on the substrate. Since water is necessary for the reaction to proceed, the heating step should be carried out in a water vapor containing atmosphere. In general, an atmosphere having a relative humidity of at least about is desirable although not critical to the operability of the process with a relative humidity of from 90 to 100% being preferred.

Any solid substrate may be coated by the process of the instant invention since the only criteria is that it be capable of supporting the metal oxide coating. Nonmetallic substrates such as glass, paper or wood are conveniently coated by the instant process. In addition, plastic materials such as for example, polyethylene, polypropylene, polyvinyl chloride and Mylar can be coated. Metallic substrates such as brass, stainless steel and nickel may also be coated with the oxide of group III A metal by the process of the instant invention.

Besides providing a convenient method for applying a corrosion inhibiting or appearance enhancing coating to various substrates, the present process has been found to be useful in the art of electrostatographic reproduction. Certain advanced electrostatographic duplicators employ an endless belt coated with selenium or an alloy thereof as the photoreceptor. Since these belts must be flexible and have the strength to withstand the rigors imposed upon them during the duplicating process, nickel has been found to be an especially suitable material from which to manufacture such a belt. Such a flexible photoreceptor requires a layer of nonconductive material between the conductive nickel substrate and the photoconductive surface. Unlike aluminum, nickel does not readily oxidize to form a nonconductive surface coating. However, by applying an aluminum oxide coating to the nickel belt by the process of the instant invention, a nonconductive barrier between the nickel and photoconductive layer is obtained.

The method of carrying out the process of the instant invention is further illustrated by the following examples.

EXAMPLE I A flexible nickel sheet is prepared by electroplating nickel from an acid bath of nickel sulfamate onto a chromium surface and removing the deposited nickel. This sheet is then suspended in the TiCl vapors formed when liquid titanium tetrachloride is poured into a large beaker under ambient conditions of pressure, temperature and humidity. This operation is carried out in a laboratory fume hood due to the irritating nature of the TiCl, vapors. After exposure to the vapors for about 60 seconds, seconds, the nickel sheet is removed and moistened by exposure to water vapor, at which point particulate (+400 600 mesh) aluminum hydroxide is cascaded over it. The nickel sheet, bearing a relatively uniform coating of TiCl, and Al(OH) is placed in an oven at a temperature of 100C. and relative humidity of for 2 minutes. Upon removal of the nickel, a uniform coating of aluminum oxide is observed in the treated areas. The chemistry involved in the process is complex, and it is not known whether aluminum oxide is deposited directly or whether metallic aluminum is deposited and immediately oxidized by atmospheric oxygen.

Five nickel sheets treated in the above manner are tested by the method disclosed by M. S. Hunter and P. E. Fowle in J. Electrochem. Soc. 101, No. 9, (1954) Pp. 481-485. This method, which determines the barrier thickness of A1 0 in terms of oxide barrier units (OBU) indicates that the 5 sheets tested have barrier layers ranging from 19.5 to 24.9 A in thickness.

EXAMPLE ll A sheet of Mylar film is treated with TiCl, and Al- (OH) as described in Example 1. Upon heating in the previously described manner, a uniform layer of aluminum oxide is observed on the film.

EXAMPLE Ill A stainless steel plate is contacted with fumes of SnCl which result when liquid stannic tetrachloride is poured into a large beaker in a laboratory fume hood. The plate is then moistened by blowing saturated air over it and dipped into particulate aluminum hydroxide. The so-treated plate is placed in an oven at C. and 40% relative humidity for 3 minutes. Upon removal from the oven, the plate is observed to have a regular layer of aluminum oxide on its surface.

EXAMPLE IV A stainless steel slug is contacted with fumes of PtCl, in the manner previously described. After such contact, the slug is cascaded with particulate gallium hydroxide. After heating at C. in an atmosphere having a relative humidity of 35% for 2 minutes, a layer of gallium oxide is observed on the steel slug.

EXAMPLE v The procedure of Example I is repeated using titanium trichloride and thallium hydroxide to form a layer of thallium oxide on the substrate.

EXAMPLE VI The procedure of Example I is repeated using indium hydroxide and titanium tetrachloride to form a layer of indium oxide on the substrate.

What is claimed is:

1. A method of coating a substrate with an oxide of aluminum, gallium, indium or thallium which comprises applying to the substrate in any order or simultaneously:

a. fumes of a metallic polychloride selected from the group of titanium tetrachloride, titanium trichloride, stannic tetrachloride, platinum tetrachloride or a mixture thereof;

b. a metal hydroxide selected from the group of one or more of the hydroxides of aluminum, gallium, indium or thallium to form a layer of the metal hydroxide in contact with the metallic polychloride on the substrate; and

c. following the step or steps of treating the substrate by the step of heating the treated substrate in a water vapor bearing atmosphere to a temperature sufficient to decompose the metal hydroxide and thereby form a layer of the metal oxide or oxides corresponding to the metal or metals of the metal hydroxide or hydroxides on the substrate.

2. The method of claim 1 wherein the substrate is contacted with the metallic polychloride before contact with the metal hydroxide.

3. The method of claim 1 wherein the substrate is simidity is from 90 to 100%. multaneously contacted with the metallic polychloride 11. The method of claim 1 wherein the substrate is and the metal hydroxide. a metal.

4. The method of claim 1 wherein the substrate is 12. The method of claim 11 wherein the substrate is contacted with the metal hydroxide before contact with 5 nickel. metallic polychloride. 13. A method of coating a nickel substrate with alu- 5. The method of claim 1 wherein the metallic polyminum oxide which comprises: chloride is titanium tetrachloride and the metal hydroxa. contacting the substrate with fumes of titanium tetide is aluminum hydroxide. rachloride;

6. The method of claim 1 wherein the substrate is b. contacting the substrate with particulate aluminum contacted with the fumes of the metallic polychloride hydroxide to form a layer of aluminum hydroxide for a period of at least about 60 seconds. in contact with the titanium tetrachloride on the 7. The method of claim 1 wherein the treated subsurface of the substrate; and strate is heated to a temperature of from 50 to 150C. c. heating the treated substrate to a temperature of 8. The method of claim 7 wherein the heating is car- 15 from 50 to 150C. in a water vapor bearing atmoried out for a period of at least about 1 minute. sphere having a relative humidity of at least 30% 9. The method of claim 1 wherein the heating is carfor a time sufficient to decompose the metal hyried out in an atmosphere having a relative humidity of droxide and thereby form a layer of aluminum at least about 30%. oxide on the substrate.

10. The method of claim 9 wherein the relative hu- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,895,131

DATED 3 July 15, 1975 INVENTOR(S) William Gerard Herbert It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 2, line 24, --afroementioned-- should be "aforementioned".

Column 2, line 40, --tetrachlorideshould be "polychloride" Column 3, line 18, "a" should be inserted before llofll "group" Column 3, 'line 55, 60 seconds, seconds, the-- should be "60 seconds, the" Signed and Scaled this seventh Day Of 0ct0b-er1975 [SEAL] Attest.

RUTH C. MRSON C. MARSHALL DANN' Arresting Officer (ummissimzer oj'Palents and Trademarks 

1. A METHOD OF COATING A SUBSTRATE WITH AN OXIDE OF ALUMINUM, GALLIUM, INDIUM OR TALLIUM WHICH COMPRISES APPLYING TO THE SUBSTRATE IN ANY ORDER OR SIMULTANEOUSLY: A. FUMES OF A METALLIC POLYCHLORIDE SELECTED FROM THE GROUP OF TITANIUM TETRACHLORIDE, TITANIUM TRICHLORIDE, STANNIC TETRACHLORIDE, PLATINUM TETRACHLORIDE OR A MIXTURE THEREOF, B. A METAL HYDROXIDE SELECTED FROM THE GROUP OF ONE OR MORE OF THE HYDROXIDES OF ALUMINUM, GALLIUM, INDIUM OR THALLIUM TO FORM A LAYER OF THE METAL HYDROXIDE IN CONTACT WITH THE METALLIC POLYCHLORIDE ON THE SUBSTRATE, AND C. FOLLOWING THE STEP OR STEPS OF TREATING THE SUBSTRATE BY THE STEP OF HEATING THE TREATED SUBSTRATE IN A WATER VAPOR BEARING ATMOSPHERE TO A TEMPERATURE SUFFICIENT TO DECOMPOSE THE METAL HYDROXIDE AND THEREBY FORM A LAYER OF THE METAL OXIDE OR OXIDES CORRESPONDING TO THE METAL OR METALS OF THE METAL HYDROXIDE OR HYDROXIDES ON THE SUBSTRATE.
 2. The method of claim 1 wherein the substrate is contacted with the metallic polychloride before contact with the metal hydroxide.
 3. The method of claim 1 wherein the substrate is simultaneously contacted with the metallic polychloride and the metal hydroxide.
 4. The method of claim 1 wherein the substrate is contacted with the metal hydroxide before contact with metallic polychloride.
 5. The method of claim 1 wherein the metallic polychloride is titanium tetrachloride and the metal hydroxide is aluminum hydroxide.
 6. The method of claim 1 wherein the substrate is contacted with the fumes of the metallic polychloride for a period of at least about 60 seconds.
 7. The method of claim 1 wherein the treated substrate is heated to a temperature of from 50* to 150*C.
 8. The method of claim 7 wherein the heating is carried out for a period of at least about 1 minute.
 9. The method of claim 1 wherein the heating is carried out in an atmosphere having a relative humidity of at least about 30%.
 10. The method of claim 9 wherein the relative humidity is from 90 to 100%.
 11. The method of claim 1 wherein the substrate is a metal.
 12. The method of claim 11 wherein the substrate is nickel.
 13. A method of coating a nickel substrate with aluminum oxide which comprises: a. contacting the substrate with fumes of titanium tetrachloride; b. contacting the substrate with particulate aluminum hydroxide to form a layer of aluminum hydroxide in contact with the titanium tetrachloride on the surface of the substrate; and c. heating the treated substrate to a temperature of from 50* to 150*C. in a water vapor bearing atmosphere having a relative humidity of at least 30% for a tIme sufficient to decompose the metal hydroxide and thereby form a layer of aluminum oxide on the substrate. 